Single photon emission computed tomography (SPECT) has become an important diagnostic tool in cardiovascular nuclear medicine. While most cardiac SPECT procedures are accomplished using a large field- of-view rotating gamma camera with a general purpose parallel-hole collimator, for a small organ like the heart, a converging geometry can be utilized to improve the geometric efficiency and resolution of projection images. Combining converging collimation with a multi-detector SPECT system offers an additional advantage of simultaneous transmission-emission tomography capability that can attenuation correct cardiac images with no increase in patient imaging time. This offers improved spatial and contrast resolution of cardiac images and improved quantification of radiopharmaceutical uptake which is important for better diagnosis of coronary artery disease, including better detection of myocardial infarction and diagnosis of ischemic heart disease and for performing physiologic imaging as is possible only with PET at the present. This proposal seeks to provide a systematic quantitative evaluation of simultaneous transmission-emission tomography for three types of detection geometries on a single-detector and a three-detector SPECT system. In particular, comparisons will be made between parallel, fan-beam, and cone-beam geometries for advantages and disadvantages in terms of image quality, resolution, specificity and sensitivity of lesion detection, and quantification of radiopharmaceutical uptake. This proposal aims to apply converging collimation to cardiac imaging using both single-detector and three-detector SPECT systems, to evaluate various transmission sources for these collimators, and to develop new algorithms that reconstruct three-dimensional images of the heart without artifacts from projections obtained using these collimators and transmission sources. It is anticipated that from the proposed research the following will be accomplished: (l) New algorithms for variable focal point detector geometries and orbit modulated sampling. (2) Improved truncated transmission reconstructions. (3) More accurate attenuation coefficient distribution by more exact energy mapping. (4) Reconstruction of attenuation and 3D collimator geometric response corrected cardiac images in reasonable clinical processing times. (5) Reconstruction of 3D scatter corrected cardiac images using new models of 3D scatter response for variable attenuation media. (6) Evaluation of combined fan-beam and cone-beam tomography on a three-detector SPECT system. (7) Results of a cardiac patient ROC study comparing fan-beam simultaneous transmission-emission attenuation-corrected cardiac SPECT with conventional parallel hole collimator cardiac SPECT. The proposed research will provide the scientific basis for establishing guidelines for the selection and specification of collimators, transmission sources, and algorithms. This research ultimately will improve patient care without any cost increase by using present cardiac SPECT procedures.